Fig. 4From: Preparation and Specific Capacitance Properties of Sulfur, Nitrogen Co-Doped Graphene Quantum DotsXPS spectra of the as-prepared samples: a survey spectra, b and c high resolution of N 1 s, and S 2p, respectively. (I) GQDs, (II) S, N-GQDs-1, (III) S, N-GQDs-2, and (IV) S, N-GQDs-3Back to article page